Increasing the delay made no difference unfortunately. However I have discovered that I get a perfect Sine Wave starting at 0,0 when I first start up the IDE, plug in the UNO then press the button. The only way to avoid losing the first point is to close down the IDE, unplug the UNO and start again. There are obviously anomalies, but at least I have a process to get the Sine Wave I want. Thanks again!